BACILLUS ANTHRACIS, a cause of lethal human infection and a bioterrorist weapon, has 2 essential virulence factors without either of which it is not pathogenic for humans. These factors are the anthrax toxin, and the capsule. The toxin is composed of 3 proteins: Lethal Factor (LF), Edema Factor (EF) and Protective Antigen (PA), each by itself non toxic. PA is the toxin part that binds to mammalian cells. A 20 KDa peptide must be hydrolyzed off PA, exposing a site to which LF or EF may bind, rendering toxins that enzymatically modify substrates in the mammalian cell cytosol. The capsule is composed of poly-D-gamma-glutamic acid (PGA).It is non-immunogenic and its protective effect unknown. The licensed vaccine is safe and protective but has limitations that justify development of improved vaccines. A recombinant PA was isolated from an uncapsulated strain. Several formulations with formaldehyde treated and alum adsorbed materials were found to be immunogenic in mice. Clinical evaluation of these formulations has begun. The capsule has been isolated from a non toxic strain and it or corresponding synthetic peptides were bound to BSA, rEPA or rPA. To identify the optimal construct peptides of varying lengths: 5, 10 and 20-mers, of D or L configuration with active groups at the C or N terminus were conjugated. The conjugates were characterized by physico-chemical and immunological assays and immunogenicity in 5-6 week old mice. Opposed to PGA alone all conjugates were immunogenic and the PGA induced antibodies were opsonophagocytic. rPA was the most effective carrier. Additional conjugation methods yielded conjugates immunogenic in mice, inducing levels not statistically different from those described in our publication. Dose response experiments of an rPA-PGA conjugate, with doses between 0.31 and 20 mcg/mouse showed 1.25-2.5 mcg to be optimal for a PGA response, while PA antibody levels increased with higher immunizing doses. The use of alum adjuvant increased PA antibody levels while having little effect upon anti-PGA levels. SEROSURVEY OF ARMED FORCES PERSONNEL IMMUNIZED WITH THE LICENSED ANTHRAX VACCINE: A survey was made of IgG antibodies in 246 sera sets at the U.S. Armed Forces Repository, taken from Armed Forces Personnel immunized with the FDA-licensed Anthrax Vaccine Adsorbed (AVA). Paired sera from HIV-negative personnel before and after the 3rd, 4th, and 6th injections were assayed by ELISA using purified Protective Antigen (PA) from Bacillus anthracis. The personnel were stratified according to sex and age (18-24 years and >24 years). Serum conversion rates of >= 4-fold increase in antibody levels were: pre-post 3rd, 85.3%; pre 4th-post 4th, 67.9%; and pre 6th-post 6th, 45%. Geometric mean levels of all individuals were 59.9 mcg/mL following the 3rd injection, 157.4 mcg/mL following the 4th, and 277 mcg/mL following the 6th. The levels were similar between the males and females but the GMC was statistically significantly higher for the younger vs. the older group. These values will be used to evaluate the IgG anti-PA levels induced by our investigational B. anthracis vaccines. PLASMODIUM FALCIPARUM: Malaria is a leading cause of morbidity and mortality globally, especially in children, estimated to cause over a million childhood deaths annually. P. falciparum causes the most severe form of disease. Experimental vaccines have been described and some tested clinically but no licensed vaccine is available. The most studied is the circumsporozoite protein (CS), expressed extracellularly on the sporozoite, and various forms of its synthesized repeat unit, NANP. These vaccines were safe and immunogenic but poorly protective, even when administered with adjuvants. Based on our studies with peptides of the B. anthracis capsule, peptides of 4 repeat units of NANP were synthesized and bound to carrier proteins and their immunogenicity studied in general purpose mice without adjuvants and by a scheme relevant for humans. Preliminary results showed high levels of antibodies, with circumsporozoite neutralizing activity roughly correlated to levels measured by ELISA. In another approach to provide a transmission blocking vaccine PFS25, a low molecular weight protein, was bound to carrier proteins and injected into mice to evaluate their antibody responses.